This application addresses the question how cells of the microvasculature interact with the extracellular matrix under conditions of normal growth and in pathologic conditions. The Principal Investigator has previously described that ECM proteins such as collagen contain cryptic integrin binding sites that may be exposed in response to tissue injury, primarily through the actions of collagenases that cleave the collagen triple helix and expose RGD sites. This observation has led to the central hypothesis of the grant, namely that exposure of cryptic RGD and non-RGD sites within the ECM represent novel signals that regulate microvascular cellular responses following ECM damage. These integrin binding sites may mediate arteriolar vasoactivity, influence leukocyte targeting and activation, influence cell proliferation and promote endothelial cell invasion of injured tissue. As discussed the Principal Investigator has generated preliminary results to suggest that in vitro all of these responses may be seen. An additional hypothesis to be tested in this application is that the injury induced protein ostepontin also expresses novel non RGD integrin binding domains; therefore, the expression of osteopontin may be important for regulation of altered functional and growth responses of the microvasculature in injury. The specific aims to be tested are: 1) to identify and characterize RGD containing sites and peptides generated from collagen type I following proteolysis that are biologically active and exhibit an ability to regulate arteriolar vasomotor tone, leukocyte diapedesis, vascular cell proliferation and endothelial cell invasion; and 2) to identify and characterize novel binding sites within osteopontin that regulate arteriolar vasoactivity, leukocyte adhesion and diapedesis, vascular cell proliferation and endothelial cell invasion. These aims are designed to yield new information concerning the role of biologically active ECM-derived peptide signals. These signals may play an important role during tissue injury by influencing microvascular cellular responses such as arteriolar vasoactivity, leukocyte diapedesis, vascular cell proliferation and endothelial cell invasion.